Tried and Tested or Mutated and New – How Plants Find Their Way
Imagine this scenario:
You're a plant. You’re growing in a sunny spot, your roots are deep in the soil, and you're busy photosynthesising – everything is going as usual. But then, suddenly, something happens: a tiny error while copying your genetic information – a mutation! Just like that, you’ve developed a new trait – that means a new characteristic, like how tall you grow or how well you resist pests. Maybe you grow a little faster? Maybe not? Or it may be that you stop growing entirely? Or something completely different: maybe you’ve suddenly (and luckily) gained the ability to fight off a disease – or (unfortunately) lost it. So, what now?
Mutations – When the construction plan changes
Mutations are spontaneous changes in DNA – the genetic blueprint of every living organism. They can occur through errors during cell division or due to outside influences like UV radiation. In plants, mutations can lead to all sorts of changes: a tomato grows larger, a grass species suddenly tolerates salt, or a flower blooms in a new colour.
Such changes happen all the time – but they are not automatically good or bad. Some are harmless, others harmful, and a few offer an advantage, providing exactly what a plant needs to survive and thrive.
Selection – When the environment has a say
So, what stays and what disappears? That’s where natural selection comes in. Think of it like a filter: traits that are useful under current environmental conditions (such as temperature, water availability, soil quality, light levels, pathogens and pests, or competition from other plants) tend to persist. Everything else gradually gets filtered out over generations.
There are different types of selection:
1. Positive selection: A new mutation gives the plant an advantage. This plant survives and reproduces more, so the frequency of this mutation increases.
Example: Due to a mutation, a plant has better drought resistance or more protection against parasites. During a drought period or in the event of a parasite infestation, all other plants that do not have this mutation suffer – some may even die. The plant with the mutation, however, survives these conditions more successfully.
2. Stabilising selection: The tried and tested remains. Changes offer no advantage – on the contrary, they may even be harmful. The mutation is filtered out.
Example: Due to a mutation, a plant produces many more fruits than the other plants. As a result, it also needs much more water and other nutrients to survive. The branches might also not be strong enough to carry so much weight. Because this mutation brings no real benefit to the plant itself, it is selected against and eventually disappears.
3. Disruptive selection: Extreme versions of a trait prevail, while the middle ground disappears completely. This happens, for example, when natural selection favors alternate phenotypes – either through adaptation to fluctuating environmental conditions or temporal changes.
Example from the animal world: The peppered moth has two forms – a black form and a white form. The white form is well-camouflaged on trees with light bark or bark covered in lichens. Due to air pollution, the lichens suffered and the white moths were not as well camouflaged on trees in highly polluted areas. However, the black peppered moths were able to hide much better from predators on trees in the polluted areas. Depending on the environment, one morph is favored over the other. As a result, two colour forms of the peppered moth still exist today – light and dark, but nothing in between.
Evolution has no masterplan – It’s a process
While some mutations clearly help plants adapt to new challenges, others are simply random changes with no real effect. In some cases, it may even be better if nothing changes at all – and the original genes and functions are kept just as they are.
Evolution is not a goal-driven process – and there is no set plan. It's a mix of coincidence, environmental conditions, and whatever manages to prevail.
In my research, I’m investigating exactly this interplay and the genetic mutations that have emerged and persisted over time through evolutionary processes. I focus on resistance genes in the wild tomato (Solanum pennellii) – a close relative of today’s cultivated tomato, now a global staple food. Among the key questions I’m exploring are a) how strong the selection pressure has been (and still is), b) the geographical distribution of natural variation at these genes and c) which genes show strong conservation versus strong diversifying selection.
Ultimately, it’s about understanding when a genetic "upgrade" truly gave the plant an advantage – and when sticking with the tried and tested turned out to be the better strategy. Or, to put it another way: "Never change a winning gene!"
Planter’s Punch
Under the heading Planter’s Punch we present each month one special aspect of the CEPLAS research programme. All contributions are prepared by our early career researchers.
About the author
Laura Randarevitch is a PhD student at the Institute of Population Genetics at Heinrich Heine University in Düsseldorf. At this university, she first studied biology and then chose the Quantitative Biology programme. In 2021, she joined the CEPLAS graduate school. In her current project, she is working on the evolution of resistance genes in Solanum pennelli, a wild tomato native to the Andes.